The main objective of the present proposal is to determine the cell biological mechanisms involved in changes in synaptic and dendritic morphology in the midbrain that accompany estrogen effects on female reproductive behavior, i.e., lordosis. The proposed studies focus on the specific neuronal circuit between the ventromedial nucleus (VMN) of the hypothalamus and the midbrain central gray (MCG). Estrogen may stimulate RNA and protein synthetic mechanisms in the VMN, resulting in the production of a polypeptide, which is packaged in a typical secretory fashion and transported down axons of VMN neurons to the MCG, where it may act as a trophic factor in the pathway for lordosis. The proposed trophic factor may induce biochemical and morphological alterations in synapses and dendrites in the MCG, which in turn may alter synaptic efficacy and neural circuitry, respectively. Three aspects of this hypothesis will be addressed. One will be to determine whether RNA and protein synthesis in VMN neurons and axonal transport in VMN axons are required for estrogen- induced alterations in synaptic morphology in the MCG. This possibility will be tested by infusing inhibitors of RNA and protein synthesis or colchicine, respectively, into the VMN and examining the ultrastructure of synapses in the MCG of animals which have received subsequent estrogen treatment. The effect of estrogen on the transport of the potential trophic factor, prolactin, will be examined using electron microscopic (EM) immunocytochemistry. The second will be to examine the morphological and biochemical mechanisms underlying the estrogen-induced alterations in synaptic structures in the MCG. For the morphological studies, the sequence of estrogen-induced synaptic alterations which may lead to an increase in synaptic number will the examined by EM. For the biochemical studies, the dependence on estrogen of the phosphorylation state of specific proteins in MCG synapses will be examined using subcellular fractionation techniques, in vitro phosphorylation, and SDS-gel autoradiography. The third way will be to determine if estrogen induces a protein implicated in dendritic development in the MCG (and VMN). Antibodies to microtubule-associated proteins will be used for EM immunocytochemistry. Fundamental studies on the morphological and biochemical correlates of a well-defined mammalian behavior, such as lordosis, will contribute to an understanding of the neuroendocrine and cell biological mechanisms involved in other complex behaviors and their aberrations.